Remove warnings and unused code

Author: rafaelfranca

activerecord/test/cases/connection_pool_test.rb

@@ -225,7 +225,7 @@ def test_checkout_fairness
         threads = expected.map do |i|
           t = Thread.new {
             begin
-              conn = @pool.checkout # never checked back in
+              @pool.checkout # never checked back in
               mutex.synchronize { order << i }
             rescue => e
               mutex.synchronize { errors << e }
@@ -262,7 +262,7 @@ def test_checkout_fairness_by_group
         make_thread = proc do |i|
           t = Thread.new {
             begin
-              conn = @pool.checkout # never checked back in
+              @pool.checkout # never checked back in
               mutex.synchronize { successes << i }
             rescue => e
               mutex.synchronize { errors << e }

activerecord/test/cases/query_cache_test.rb

@@ -151,11 +151,6 @@ def test_cache_is_flat
   end
 
   def test_cache_does_not_wrap_string_results_in_arrays
-    if current_adapter?(:SQLite3Adapter)
-      require 'sqlite3/version'
-      sqlite3_version = RUBY_PLATFORM =~ /java/ ? Jdbc::SQLite3::VERSION : SQLite3::VERSION
-    end
-
     Task.cache do
       # Oracle adapter returns count() as Fixnum or Float
       if current_adapter?(:OracleAdapter)